A. Field of the Invention
The invention relates to the electrolytic reduction of hydroxybenzaldehydes to produce the corresponding 1,2-bis(hydroxyphenyl)ethane-1,2-diol (dihydroxybenzoin). More particularly, the invention relates to the electrolytic reductive coupling of hydroxybenzaldehydes by electrolysis in an aqueous electrolysis medium in an undivided electrolytic cell to produce 1,2-bis(hydroxyphenyl)ethane-1,2-diols, and to the recovery of the product diol.
B. The Prior Art
Electrolytic reductive coupling of hydroxybenzaldehydes to prepare the corresponding 1,2-bis(hydroxyphenyl) ethane-1,2-diols has previously been accomplished in good yields. See, for example, Grimshaw et al., Journal of the Chemical Society (C), 653 (1966). However, each of the methods described in the prior art employed a divided cell. A divided cell is inherently more complex than an individed cell, thereby involving higher costs in cell construction. A divided cell exhibits a higher internal resistance than an undivided cell resulting in substantially higher power costs. Efforts to adapt such divided-cell electrolytic methods of preparing 1,2-bis(hydroxyphenyl)ethane-1,2-diols to commercial production on a large technical scale have been severely limited by the above considerations.
One of the difficulties initially encountered in the use of undivided cells for such electrolytic reductive coupling was that recovery of the product diol from the electrolytic solution was cumbersome, slow, and in practice resulted in destruction of the effectiveness of the electrolyte solution from which the product diols were extracted.
A practical combination of a workable undivided cell electrolytic reductive coupling process for the preparation of 1,2-bis(hydroxyphenyl)ethane-1,2-diol with an effective recovery of the diol in such a manner as to permit reuse of the solution from which the product diol is recovered, would be a significant advance in the art and is an object of this invention.